does anyone know of a list of things that can cause this infamous "limp mode?"

i just went back to my stock ECU and no matter what i do, i can't get it out of limp mode and it is extremely annoying to drive it at less than 20% throttle. if i try to give it more than 20% throttle, the ECU just turns the injectors OFF until i let off the throttle and get it below 20%.

every thread i have found about this is just full of people posting "oh, yeah, X sensor might cause limp mode," and such.

is there actually a definitive list of what causes this elusive LIMP MODE? i can't seem to find any mention of it in the FSM...

 

I know codes 26 and 27 (OMP) and code 45 (charge control) will put you into limp.
I think 20 (OMP sensor) will give a similar symptom, but timing isn't fixed.
Have you pulled the codes?

 

Its spelled out pretty good in the service highlights manual.

Off the top of my head:

Fuel pump relays (both of them, re-wire your pump?), as mentioned OMP, sensors to include MAP and TPS, the enrichment solenoid (one connected to FPR), injector (obviously secondary injector if its running at all)

Also there are at least 2 versions of limp mode that I have run into.

 

hmm, interesting. where can i get the service highlights manual? all i can seem to find is the FSM and Z wiring diagram.

also, the ecu will kick into limp mode for the fuel pump relays? and yes, i have rewired my pump for the time being.

any more info on this would be greatly appreciated, slo.

 

sent you a PM,

service highlight (also in sticky at top of thread).

http://www.wrex-racing.com/docs/fd/9...highlights.pdf

 

Will an overheating car or the "add coolant" buzzer make the car go in limp mode?

Had a coolant hose burst last night, then i tried to rush home, car backfired and bucked slightly if i tried to go past 4k rpm. Then check engine light came on. Funny thing is that the CEL light went away, then i could rev past 4k, then 2 minutes later i couldnt and the CEL light came back and did this til my ride home.

Also, once car goes in limp mode, does that mean you need to reset the ECU?

 

My experience with the OMP feedback circuit failure code is that you do not need to reset the ECU to get it out of limp mode. It will clear itself if the problem goes away.

 

No

Yes, but you also need to see what code is stored from the CEL coming on.

 

Limp mode is a lack of timing advance and fuel whenever the manifold sees positive pressure (or doesn't see vacuum). My experience is that you can rev or accelerate slowly to any rpm as long as there is vaccum in the manifold.
What your describing doesn't sound like limp mode, and a coolant level sensor buzzer won't cause it.

 

This is the hose i broke last night..



I did the TB bypass like a year or so ago with a brass barb adapter. After finding out this is the hose that broke, i looked for the connector and its no where to be seen.

All i know is ALL the coolant in my system came out of those 2 open ends and sprayed coolant everywhere. I saw steam coming out my hood, add coolant buzzer on, fans on FULL blast last night which made me go bananas.

Now that i know this is the hose to fix again. My concern is why the CEL went on. Im gonna have to pull the code but right now its dark and im just sitting where wondering what could it be?

The CEL only came on last night during all this mayhem. Could it be all the coolant that was spewing out hit an electrical connection? Maybe the TPS?

Btw, the CEL is not staying on. It came on like 3 times last night, then went off, in like 2 minute intervals.

 

Ok i pulled the codes.

3 codes came up

40 Solenoid valve - purge control (auxilary port valve)

42 Solenoid valve - turbo precontrol

43 Solenoid valve - wastegate control


Now its starting to become clear. All 3 codes are related to the turbos. Our turbos are coolant cooled. My only assumption is since i lost all the coolant, maybe thats why my CEL came on?

I still dont know why my car bucked at around 4k rpm at times. Im guessing since im non seq and thats when the turbos start spooling up. I have no clue.

 

Those solenoids are under the intake manifold...not too far from where the hose is located. Wouldn't surprise me if their electrical connectors got wet and the ECU freaked out since it was seeing higher or lower resistance on those circuits than it should. Resistance is the only way the ECU has of knowing if something has run amok for those particular outputs.

 

Thanks for the info.

So what should i do now? Besides try my best to make sure the entire engine bay is dry before i fire it up again.

Should i reset the ECU?

 

yes reset the ecu. they will only throw codes for open or shorted.

 

terribly old thread.....


i got another FD that is currently hitting the infamous limp mode.

i browsed through the FSM highlights and found every CEL code that will trigger the hard limp mode for boost:

 

i can confirm that any of the fuel or boost related codes cause a cut @1psi.

i think in wiring up my FC-REW i have seen all of the fuel pump relay, fuel pump resistor and boost solenoid codes.

they are definite cuts too, car runs great up to ~1psi and then will just stop.

the pressure sensor, i have also had issues with, and the ECU will just run a fixed value, so its not really a cut. if you were to unplug the pressure sensor, car will idle rich, and then as you push the gas, the mixture gets better until to you too far and then its too lean, and stops running (way before you hit boost)

 

so I’m running into the same issue right now, I reset the ecu and looks like I’m getting low voltage to one of the pins for the circuit relay so I jumped it and after resetting the ecu it worked great went into boost etc. however after going down the street for gas after I cut off the car and filled up on the way back it starting sputtering and bucking at me if I went into boost like you’re seeing.

 

What circuit relay? Did you pull the code(s)?

 

The Circuit relay in the engine bay right next to the EGI main relay. I tried to pull the codes buy using the diagnostic box by putting a jumper wire in the TEN/GND and turning the key to the on position but I did not see any CEL where i could pull the code. I have a JDM 94 fd so I was looking at the dash and didnt see any lights pop up and the lights that did, didn't flash.

 

IIRC JDM doesn’t generate a CEL dash light. I’d do a search on how to pull those codes, but in my experience it’s usually OMP related in some way…

https://www.rx7club.com/3rd-generati...jdm-fd-664425/

 

thanks! I’ll be getting the things I need to be able to pull the codes but my situation is a little strange, right now I have the circuit relay out and have a jumper in it and with out that jumper in the ecu isn’t telling the fp to send fuel and won’t turn over. Which is where I’m thinking it’s more of an electrical issue but I’m curious to see what codes come up.